Over the years civil engineers, in particular, and others, have become very sensitive to the necessity of monitoring pressures existing or developing underground in all manner of man's constructions. Such necessity has mothered a family of transducers useful to measure from a remote station pore pressures in the earth, differential pressures, and various hydraulic and pneumatic conditions underground and normally inaccessible. It is desirable that such measurements be made or data collected over long periods of time, years, in fact, so that progressive changes taking place underground may be evaluated and charted. Thus, primary characteristics required in such transducers are long-term stability, ruggedness, sensitivity, and repeatable accuracy. It is a prime object of this invention to provide a transducer that has such characteristics.
The art of transducers displays a wide variety of devices useful in underground measurement systems but which, for one reason or another, are less than fully satisfactory. Heretofore, pressure-actuated mechanical valves have been proposed without fully satisfying the need. Usually such valves include metal parts particularly subject to corrosion, tending to cause the transducers to malfunction. Other transducers have included diaphragm-shielded and diaphragm-actuated valve elements. These have in part been successful for a time, but it has been noted that their initial accuracy decays with the passage of time, due undoubtedly to wear and age. It has been another important object of this invention to provide a transducer of the diaphragm type which overcomes the earlier problems by avoiding the use of inherently inaccurate mechanical linkage means or probes for valve-actuating purposes.
It has been observed that many prior transducers that have suffered from the problems already mentioned have included a spring-pressed mechanical ball which must be unseated for proper functioning of the transducers. Springs are notoriously troublesome, especially in metallicly unwholesome environments under compression for long periods of time and, where they are small, subject to fatigue and relatively non-linear in their functions. Thus, another object of this invention has been to produce a transducer that includes no metal springs or valve balls or metallic seats subject to the corrosive and debilitating effects of their underground environment. A still further object of this invention has been the provision of a rugged, inexpensive and compact transducer that can be easily manufactured wholly of inert and largely man-made synthetic materials not normally affected by oxidation, corrosion or fatigue.
The objects and advantages stated and others will become apparent during the course of the following detailed description of a preferred embodiment of this transducer invention.